1. Field of the Invention
The present invention relates to novel methods for the functionalization of polyaromatic polymers to modify the chemical and mechanical properties thereof and the resultant polyaromatic polymer derivatives.
2. Description of the Prior Art
Synthetic polymers and engineering plastics have found widespread use in the manufacturing industry for their excellent processability and bulk physical properties. Most such polymers have excellent physical properties such as thermal and long-term stability, resistance to radiation, wear, abrasion, chemical -solvents and low toxicity. These polymers exhibit good mechanical strength.
Most of the engineering polymers also exhibit undesirable properties at the polymer surface or interface. Thus, the surfaces of articles constructed of most of the synthetic engineering plastics are hydrophobic, non-wettable and of low biocompatibility. The polymer art has, therefore, sought ways of modifying the surface properties and characteristics of these materials to suit their anticipated application.
An early method [Gregor et al, J. Applied Polymer Sci., Vol. 30, pages 1113-1132 (1985); and U.S. Pat. No. 4,705,753] for modifying or derivatizing polymer surfaces involved the introduction of a comonomer bearing desirable functional groups to the monomer precursor of the primary hydrophobic engineering polymer. This method necessarily results, however, in a copolymer whose backbone is substantially different from the homopolymer and frequently provides a material with less than optimum performance characteristics.
A more fundamental approach involves the use of a physical blend of polymers, one of which is the so-called xe2x80x9cfunctionalxe2x80x9d polymer whose desirable properties and pendant functional groups will be evident at the bulk polymer interface or, in the case where the polymer has been made into an is article of manufacture, at that article""s surface. This technique, besides invariably producing a different material, performance-wise also suffers from limitations involving the physical compatibility of the two types of polymers. Few pairs of polymers are sufficiently compatible to be blended successfully. In this respect, even the molecular weight distribution of one of the components may play a critical role. Even after a suitable pair has been found, the distribution of the functional polymer component over the polymer surface is hard to predict or control. Moreover, such blends are susceptible to phase separation resulting in the removal of the functional component over the course of ordinary use. A number of issued patents describe these blending techniques. See, e.g., U.S. Pat. Nos. 3,629,170; 3,781,381 and 4,387,187. A variation involving an additional cross-linking step is discussed in U.S. Pat. No. 4,596,858 and in Gryte et al, J. Applied Polymer Sci., Vol. 23, pages 2611-2625 (1979).
Another method proposes the grafting of a second polymer onto the surface of the manufactured article. This method requires polymerizing the monomer precursor of the second polymer and then irradiating the engineering polymer surface with gamma, electron beam or ultraviolet radiation. British Patent No. 801,479, for instance, describes a method in which a coating material is applied onto a structural surface which is then exposed to charged particle radiation to initiate bonding between the two materials. A variation of this process is set forth in United Kingdom Patent No. 839,483 in which the bulk polymer is first subjected to ionizing radiation to activate the structural surface and then treated with a dissimilar organic coating material. Such radiation treatment can penetrate the materials to a significant depth and could be detrimental to their structural integrity. High energy radiation can also precipitate polymer degradation and chain scission.
Yet another alternative is the xe2x80x9ccompositexe2x80x9d or multi-layer approach. The strategy behind this technique is to preserve the bulk properties of the article of manufacture and its primary polymer component while introducing the desired interfacial or surface characteristics via a filler. In practice, the composite approach, although potentially the most attractive, is characterized by a tenuous, weak link at the surface of the bulk polymer and the modifying agent. This instability is particularly apparent where the two materials are simply held together by adsorptive forces.
Polyaromatic polymers have found widespread commercial applications, particularly in the area of composites, i.e., polymer matrices reinforced with a variety of inorganic fillers.
Polyarylcarbonates, for example, are increasingly being used as engineering or structural polymers. The highly hydrophobic polycarbonates, however, tend to phase separate when attempts are made to reinforce them with hydrophilic inorganic fillers such as silica due to their mutual incompatibility. Polyarylsulfone composites are finding increasing use in biomedical and other structural applications. The tendency of polyarylsulfones to degrade under in vitro and in vivo conditions, however, have limited their utility in the past. Proposals to enhance their applicability in the biomedical field by reinforcement of polyarylsulfone materials with inorganic fillers have met with limited success due to the lack of high strength interfacial bonding between the incompatible hydrophobic polyarylsulfone surfaces and the largely hydrophilic surfaces of the inorganic reinforcing fillers.
Thus, there remains a need for the covalent derivatization or modification of hydrophobic polymer surfaces, especially the surfaces of articles manufactured therefrom, under relatively mild reaction conditions. Further, it would be most advantageous if such a modification could be performed under heterogeneous conditions in which the hydrophobic polymer material is first manufactured and processed to exploit its desirable engineering properties and then exposed to a treatment which seeks to modify the surface properties of the preformed article without altering its gross structural characteristics. Most importantly, the modification must be applicable to hydrophobic polymers such as the polyarylsulfones, etc., which tend to be inert and unreactive.
It is an object of the present invention to overcome the disadvantages associated with the prior art in providing functionalized polyaromatic resins and polymers.
The above and other objects are realized by the present invention, one embodiment of which relates to a method of preparing a silane functionalized polyaromatic polymer comprising:
(a) reacting a polyaromatic polymer with a sulfonating agent to introduce sulfonic acid groups on repeat aromatic rings in the polyaromatic polymer, and
(b) reacting the product of (a) with a silane terminated coupling agent capable of undergoing a condensation reaction with the sulfonic acid groups thereof to produce a polyaromatic polymer having silane terminated groups on the repeat aromatic rings thereof; the reactions (a) and (b) being conducted under conditions which do not substantially destabilize the polyaromatic polymer.
Another embodiment of the invention is the silane functionalized polyaromatic polymer produced by the above-described method.
An additional embodiment of the invention comprises a silane functionalized polyaromatic polymer having the formula:
[Ar] xe2x80x94A xe2x80x94Si(H)x(OR)3xe2x88x92x
wherein:
Ar is a repeat aromatic ring in the polyaromatic polymer;
A is a non-reactive bridging group between Ar and Si;
R is, e.g., an alkyl group; and
x is an integer.